This invention relates to engine covers and, more particularly, to engine covers with internally-mounted vibration damping plates for noise reduction.
It is known in the art relating to engine covers to attach vibration damping plates or stiffeners to selected wall portions of the covers as needed to limit the occurrence of sound transmitting vibrations induced in the covers by operating components of the engine. The application of such damping means has generally been accomplished after design of the basic cover and the damping materials are commonly applied to the cover exterior. This allows the use of materials which could not be used in contact with hot engine oil, but it exposes the damping materials to external air, moisture and dirt which may cause deterioration of the damping materials during extended service of an associated vehicle. Sandwich-type damping materials can be utilized but must undergo time consuming durability testing to determine their potential for satisfactory service over the life of a vehicle.
The present invention provides a cover assembly for an engine wherein the cover preferably encloses a compartment in which lubricating oil and/or oil vapors are contained and wherein the cover includes at least one relatively large wall portion which is potentially subject to induced vibrations that transmit undesirable noise or sound to the exterior of the engine. To reduce the vibration and resulting noise generation of the vibration susceptible wall portions, called for convenience mounting wall portions, vibration damping plates are attached to the interior of the mounting wall portion or portions of the cover. The damping plates may be made from untreated steel since the lubricating oil atmosphere serves to protect the plates against oxidation. However, if desired, the plates may be coated or otherwise protected from oxidation and applied in cover locations wherein lubricating oil is not available for protection of the plate materials.
A preferred damping assembly at each location comprises a pair of associated damping plates, including a first damping plate having a surface directly engaging a substantial part of one of the mounting wall portions and a second damping plate having a surface directly engaging a substantial part of the first damping plate. The pair of damping plates are mechanically fastened together and to the interior of the mounting wall portion of the cover at a plurality of common fastening locations. The plates have different thicknesses with diverse vibration frequencies that are adapted to offset or reduce vibrations in the mounting wall portions of the cover over a range of engine speeds.
In a preferred embodiment, a cover assembly is designed to cover operating mechanisms of the engine. For example, the cover may be a front engine cover which encloses a timing chain drive for connecting the crankshaft with sprockets provided for driving associated overhead camshafts of an engine. Such a cover may have multiple mounting wall portions from which vibration-generated sound may be transmitted so that damping assemblies may be located at each of the mounting wall portions.
The damping assemblies preferably include a pair of damping plates having differing thicknesses and secured to the cover mounting wall portions by suitable fastening means. A preferred arrangement for an aluminum cover is to provide cast in mounting posts on which are received openings in the pairs of damping plates to secure the plates to the cover at several peripheral locations. The plates are preferably provided with upwardly angled spring portions at each of the fastening openings, and these spring portions are engaged by ends of the mounting posts, deformed by any suitable method to create heads. Each pair of plates is thus held against the associated surface of the cover with a spring bias which maintains the plates and the cover in engagement with one another and allows vibrations in the plates and cover to be damped by relative motion of the plates and cover in an oil containing atmosphere.
In an exemplary embodiment, a first plate adjacent the cover is supported by a second plate which is retained by the retainer means. The second plate is preferably thicker that the first plate, the thicknesses of the damping plates having a ratio in the range of from about 5/4 to 2/1 or, in a described embodiment, a ratio of 3/2.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
FIG. 1 is an exploded pictorial view of a front engine cover assembly for enclosing a lubricated camshaft chain drive mechanism and other components and showing the application of associated pairs of damping plates to mounting wall portions of the cover.
FIG. 2 is a cross-sectional view through one of the pairs of damping plates showing the mounting of the steel plates to a mounting post of an aluminum cover.
FIG. 3 is a pictorial view of the formed aluminum head on a mounting post shown retaining a mounting plate to the cover at one of the mounting locations.